Quasars can be used to verify the parallax zero-point of the Tycho-Gaia Astrometric Solution

Context: The Gaia project will determine positions, proper motions, and parallaxes for more than one billion stars in our Galaxy. It is known that Gaia's two telescopes are affected by a small but significant variation of the basic angle between them. Unless this variation is taken into account during data processing, e.g. using on-board metrology, it causes systematic errors in the astrometric parameters, in particular a shift in the parallax zero-point. Previously, we suggested an early reduction of Gaia data for the subset of Tycho-2 stars (Tycho-Gaia Astrometric Solution; TGAS).

Aims: We investigate whether quasars can be used to independently verify the parallax zero-point in early data reductions. This is not trivially... (More)

Context: The Gaia project will determine positions, proper motions, and parallaxes for more than one billion stars in our Galaxy. It is known that Gaia's two telescopes are affected by a small but significant variation of the basic angle between them. Unless this variation is taken into account during data processing, e.g. using on-board metrology, it causes systematic errors in the astrometric parameters, in particular a shift in the parallax zero-point. Previously, we suggested an early reduction of Gaia data for the subset of Tycho-2 stars (Tycho-Gaia Astrometric Solution; TGAS).

Aims: We investigate whether quasars can be used to independently verify the parallax zero-point in early data reductions. This is not trivially possible as the observation interval is too short to disentangle parallax and proper motion for the quasar subset.

Methods: We repeat TGAS simulations but additionally include simulated Gaia observations of quasars from ground-based surveys. All observations are simulated with basic angle variations. To obtain a full astrometric solution for the quasars in TGAS we explore the use of prior information for their proper motions.

Results: It is possible to determine the parallax zero-point for the quasars with a few μas uncertainty, and it agrees to a similar precision with the zero-point for the Tycho-2 stars. The proposed strategy is robust even for quasars exhibiting significant spurious proper motion due to a variable source structure, or when the quasar subset is contaminated with stars misidentified as quasars.

Conclusions: Using prior information about quasar proper motions we could provide an independent verification of the parallax zero-point in early solutions based on less than one year of Gaia data. (Less)

@misc{09f179f0-6f13-4c24-9371-073b1f578d35,
abstract = {Context: The Gaia project will determine positions, proper motions, and parallaxes for more than one billion stars in our Galaxy. It is known that Gaia's two telescopes are affected by a small but significant variation of the basic angle between them. Unless this variation is taken into account during data processing, e.g. using on-board metrology, it causes systematic errors in the astrometric parameters, in particular a shift in the parallax zero-point. Previously, we suggested an early reduction of Gaia data for the subset of Tycho-2 stars (Tycho-Gaia Astrometric Solution; TGAS).<br/><br>
Aims: We investigate whether quasars can be used to independently verify the parallax zero-point in early data reductions. This is not trivially possible as the observation interval is too short to disentangle parallax and proper motion for the quasar subset.<br/><br>
Methods: We repeat TGAS simulations but additionally include simulated Gaia observations of quasars from ground-based surveys. All observations are simulated with basic angle variations. To obtain a full astrometric solution for the quasars in TGAS we explore the use of prior information for their proper motions.<br/><br>
Results: It is possible to determine the parallax zero-point for the quasars with a few μas uncertainty, and it agrees to a similar precision with the zero-point for the Tycho-2 stars. The proposed strategy is robust even for quasars exhibiting significant spurious proper motion due to a variable source structure, or when the quasar subset is contaminated with stars misidentified as quasars.<br/><br>
Conclusions: Using prior information about quasar proper motions we could provide an independent verification of the parallax zero-point in early solutions based on less than one year of Gaia data.},
author = {Michalik, Daniel and Lindegren, Lennart},
issn = {0004-6361},
language = {eng},
pages = {26--26},
publisher = {ARRAY(0x8437f08)},
series = {Astronomy & Astrophysics},
title = {Quasars can be used to verify the parallax zero-point of the Tycho-Gaia Astrometric Solution},
volume = {586},
year = {2016},
}